Generally the effluent from commercial laundries is not clean enough to be discharged directly into a public water treatment plant. It may include excessive concentrations of fats, oils, and/or greases (FOGs) as well as excessive concentrations of total suspended solids (TSS), BOD, COD, heavy metals, and VOC (volatile organic compound).
One of the problems encountered in treating wastewater from commercial laundries is that different loads of laundry may contain different effluent. For example, one load of laundry may be shirts while the next is pants. Another may be shop towels and another may be floor mats. These are all treated differently and the wastewater is different from each of these types of loads. For example, shop towels produce extremely high FOGs whereas shirts may produce relatively low FOGs and mats produce high TSS. Typically the wastewater from the separate batches of laundry are discharged into a common line which leads to an equalization tank or pit.
As the name indicates, this tank allows the wastewater to equalize thereby minimizing swings in effluent contaminant with varying wash loads so that only one treatment parameter is required. The water discharged from the equalization tank would then be chemically treated, clarified and discharged. Chemical treatment and particularly the addition of the correct amount of emulsion destabilizers or coagulants is particularly dependent upon the composition of the water in the equalization tank. It is undesirable to add too little. This would not effectively break up the oil and water emulsion. Adding too much coagulant increases costs and interferes with downstream treatment of the waste stream.
Typically the laundry operator will simply monitor the effluent from the equalization tank periodically and manually adjust the feed rate of the coagulant. This requires close attention and creates a tendency to add too much coagulant.
Other systems have been developed which continuously monitor the wastewater in an attempt to continuously control the amount of coagulant added. This is disclosed, for example, in Dobrez, U.S. Pat. No. 5,160,439. The problem with such systems is that they require continuous on-line monitoring of an oil/water emulsion. These oil/water emulsions tend to foul the test probes requiring cleaning and other maintenance and accordingly are less preferred.
Accordingly it is the object of the present invention to effectively add coagulant to the wastewater of a commercial laundry. Further it is an object of the present invention to add the coagulant in response to the contaminants of the wastewater as it is dispensed from a washing apparatus.
It is also an object of the present invention to directly add other water treatment agents such as peroxide, enzymes, acids or bases and heavy metal scavengers to the effluent as needed based on content of the wash load.